1. Field of the Invention.
This invention relates to the identification and tracking of batches of objects through a manufacturing process. More specifically, it relates to a method for monitoring the progress of a plurality of batches of semiconductor wafers or memory disks through a multiplicity of processing operations at various locations within a plant facility.
2. Description of the Prior Art.
In the semiconductor manufacturing industry semiconductor wafers are moved through a manufacturing plant to a number of different locations where the semiconductor wafers are etched, cleaned, processed using photolithography operations, tested and subjected to various other manufacturing testing and processing operations. Similarly, memory disks are also moved through a sequence of manufacturing operations in a manufacturing facility.
It is common in the industry to handle the wafers or memory disks in batches contained within carriers specifically designed for the purpose of supporting the wafers or memory disks in the proper position for the manufacturing and processing machinery which may either process the disks or wafers while they remain in the carriers or removes them for a processing operation and then returns them to the carrier. A batch is defined and used hereinafter to mean one or more (up to the capacity of the carrier) of the semiconductor wafers or memory disks.
In a manufacturing plant, it is desirable to track the progress of a batch of wafers or memory disks through the manufacturing process. Heretofore this has been done on a manual basis either by generating paper records to track the progress of particular batches through the various manufacturing and processing operations or by some semi-automated system such as manual keyboard entry.
Conventional technology utilizing bar code readers and the like could also be used to provide a somewhat more convenient tracking of individual wafer carriers but the reading of the bar codes may require the reader to be placed in very close contact with the coded bar code strip and also may require the use of either visual light or infrared illumination supplied by the reader in order to provide a readout of the coded information. Additionally, bar code stickers would have to be applied to the carriers using some method. Present bar code stickers will not stick to carriers molded from Teflon or similarly slippery materials or survive the types or chemical baths in which the carriers are immersed Even attempts to place the bar code stickers in a laminate suitable to protect the sticker from the chemical baths is unsatisfactory because of possible difficulty in reading the bar codes accurately through most transparent materials and the possibility that those materials optically suitable for the job may not stick to the carriers.
It is also possible that the workers using a conventional bar code reader wand to read a coded strip on a carrier could introduce particulate contamination to the wafers or disks because of the necessity of the reader to be in very close proximity to the bar code in order to read it.
Another drawback which would be present if conventional bar code reader technology were used to provide identification of carriers is that it would not be possible to read the bar codes on the carriers if they were stored in boxes at some stage of the manufacturing and processing operations. The necessity of providing corresponding coding on the boxes themselves would be a definite drawback in the usage of a bar code method. It would therefore be quite important to the proper operation of an identification system to have the system be capable of identifying carriers where they are enclosed in shipper boxes constructed of plastic or similar materials.
Although methods of identifying objects using radio frequency interrogation of transponder tag structures have existed for the past 20 years, the application of those techniques to monitoring the progress of batches of semiconductor wafers or memory disks through processing and manufacturing operations has not heretofore occurred.
It is desirable to provide an identification and tracking system which utilizes RF interrogation of coded surface acoustic wave transponder structures to provide a means for identification and tracking of semiconductor wafer or memory disk carriers through manufacturing and processing locations within a plant.